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RE: aluminum design - seismic behavior

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Inherently aluminum is ductile, but there is nothing to quantify seismic behavior of connections in the nonlinear range. The problem is that there is no testing to substantiate a given R. Without testing of a seismic structural system there is nothing to substantiate anything other than brittle behavior. There is also nothing in any "building code" for welding procedure or other QC to assure ductile behavior of any given aluminum seismic structural system. Assuming brittle behavior (Ex: R = 1.25) is conservative, but I would be hard pressed to substantiate an R of 6 or 8. I know that I can get ductile aluminum weldments. I also know that I can get brittle aluminum weldments.

Are you aware of any aluminum seismic structural systems where a response (R value) was developed? Granted, a lot of our R values are a bit on the contrived side, but there is testing on some systems that can be extrapolated to other similar systems in steel, concrete, or wood.

I recall the pre vs. post Northridge seismic special moment frames of steel, and the poor performance. We just don't have the data on aluminum.

Regards,
Harold Sprague




From: "Jordan Truesdell, PE" <seaint(--nospam--at)truesdellengineering.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: aluminum design
Date: Mon, 31 Jan 2005 11:56:48 -0500

Why would you recommend considering aluminum as a brittle material, unless you're specifying an unusual grade/temper? Most aluminums have an Fu that is about 1.25 to 1.4 times Fy (better in some 2000 series, iirc). It's not quite "bubble gum", like 300 series stainless, and the plastic region isn't quite as flat as steel, but it does have a well documented plastic range. Admittedly, aluminum does not have a fatigue limit but that shouldn't be an issue for seismic loadings, as the number of cycles is low. Unless you're asking for castings, or specialty aluminums (Beryllium Aluminum is my favorite exotic) - none of which are economical in a building - it should perform to its material properties just fine (decent for stress, sucky for deflection).

Jordan

At 04:13 PM 1/31/2005 +0000, you wrote:
The UBC contained provisions for aluminum design, but with the code merger and the lack of representation by the aluminum industry, there are very few "building code" provisions in ASCE or IBC. There is a 2005 Aluminum Design Manual due out soon, and they too have gutted the seismic and wind provisions. When it comes to designing in aluminum, you must use first principles. For wind and snow it is not a big deal. For seismic design, you should assume a linear performance for a brittle material. That said, getting it through a plan checker might be problematic.

Regards,
Harold Sprague




From: "John J. Treff" <jjtreff(--nospam--at)hotmail.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: aluminum design
Date: Fri, 28 Jan 2005 23:48:21 +0000

Hello,
Is there such a thing as "American Institute of Aluminum Construction"? If there isn't, can any of you tell me who's the authority in the US for aluminum design? Is there a code for it?

Thank you,

JJ


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